1. Field of the Invention
The present invention relates to a liquid ejection head, and more particularly, to a liquid ejection head where a piezoelectric element is used as a pressure generating device for ejecting liquid.
2. Description of the Related Art
As an image forming apparatus, an inkjet printer (inkjet recording apparatus) is known which comprises an inkjet head (liquid ejection head) having an arrangement of a plurality of nozzles (liquid ejection ports) and which records images on a recording medium by ejecting ink (liquid) from the nozzles toward the recording medium while the inkjet head and the recording medium are caused to be moved relatively to each other.
An inkjet head in an inkjet printer of this kind has pressure generating units, each comprising, for example, a pressure chamber to which ink is supplied from an ink tank via an ink supply path, a piezoelectric element which is driven by an electric signal in accordance with image data, a diaphragm constituting a portion of the pressure chamber which is deformed by driving the piezoelectric element, and a nozzle which connects to a pressure chamber from which the ink inside the pressure chamber is ejected as a liquid droplet by means of the volume of the pressure chamber being decreased by the deformation of the diaphragm. In an inkjet recording printer, one image is formed on a recording medium by combining dots formed by ink ejected from the nozzles of the pressure generating units.
Therefore, in order to form an image of high quality in a stable fashion, it is necessary to arrange the pressure generating units at high density and to ensure reliable electrical connections in the wires that supply drive signals for driving the piezoelectric elements, and driving the piezoelectric elements stably, without obstruction of the drive of the piezoelectric elements.
In view of the above circumstances, for example, Japanese Patent Application Publication No. 6-286126 discloses an inkjet head. In the inkjet head, in order to increase the reliability of the hermetic sealing of ink ejection devices (piezoelectric elements), the ink ejection devices are connected electrically to terminal sections of a flexible cable, and are hermetically sealed by an adhesive layer in the gaps between the flexible cable and a flow channel substrate or a lid plate, or alternatively, the ink ejection devices are maintained in a hermetically sealed state by forming projecting sections of substantially the same height as the thickness of the ink ejection devices on either the flow channel substrate or the lid plate, in such a manner that they surround the perimeter of the ink ejection devices, and by bonding a flexible cable on top of the projecting sections by means of an adhesive layer.
Furthermore, Japanese Patent Application Publication No. 2002-46281 discloses an inkjet type recording head. In the inkjet type recording head, in order to improve the rigidity of the chamber partitions and to arrange pressure generating chambers at high density, a bonding substrate made of single crystal silicon is bonded to the piezoelectric element side of a flow channel formation substrate, via a sealing member, and an integrated circuit is formed in an integrated fashion on the region of the bonding substrate opposing the piezoelectric elements, on the same side as the bonding surface with the flow channel formation substrate. Conductive members are connected to the electrodes constituting the piezoelectric elements, thereby electrically connecting the piezoelectric elements and the integrated circuit, and furthermore, each piezoelectric element is sealed within a space demarcated by the bonding substrate and the sealing member.
However, in the technology described in Japanese Patent Application Publication No. 6-286126, since the flexible cable is supported substantially by the adhesive layer, contact between the flexible cable and the ejection devices may occur if the thickness of the adhesive layer decreases due to the bonding pressure, and hence the driving of the ejection devices is constricted and it may become difficult to perform stable ejection.
Furthermore, in the technology described in Japanese Patent Application Publication No. 2002-46281, the flow channel substrate and the bonding substrate are limited to being single crystal silicon, and hence there is no freedom of choice of the material, and furthermore, the sealing member is also limited to being an adhesive, glass, or silicon. Therefore, if the sealing member is constituted by adhesive only, the adhesive layer deforms due to the pressure applied in order to achieve sufficient bonding force, and there is a possibility that the bonding substrate may come into contact with the piezoelectric elements and may obstruct the driving of the piezoelectric elements. Furthermore, if a hard material such as glass or silicon is used for the sealing member, then it is difficult to curb the influence of variations in the thickness of the piezoelectric elements and the influence of variations in the height of the conducting members, and there is a possibility that suitable reliability may not be ensured in the connections with the integrated circuit.